Re: demo stream, filter questions

[Alexander Adolf <alexander.adolf@micronas.com>]

Dear Gorry, dear Colleagues,

On 2002-09-03T10:40+0100, Dr G Fairhurst wrote:

> [...]
> > What comes in mind here is that the MPE header is used as hardware
> > filtering at "MAC/Section" level also. DVB streams are normally high
> > speed streams (in the future > 100 mbps packet throughput (QAM,
> > 8PSK)).

Today 100 Mbps are reality on satellite systems. Looking into the
future I would expect the satellite operators to add some multiples to
that. One day we will probably run into physical restrictions imposed
by the earth's atmosphere. However I am not an expert on this so
please don't ask me how far we will get... ;-) And then there is still
otical fibre where you get several Gbps today.

> So... There are several questions here.
>
> 1) How significant a feature is "section filtering". I would
> be interested to know how important this feature is. As I see it,
> it gives the encapsulator the possibility of forming seperate
> logical subnetworks within the same MPEG-2 TS Logical Channel.
> Is this just feature-overload? Is there a good reason for not
> using a separate PID for each subnetwork?

Taking into account the transmission link speeds I just mentioned, a
good amount of the filtering definitely has to be done in hardware.

But apart from that, 'just' using another PID in a DVB network is not
as easy as it might seem.

As DVB networks are television broadcast networks (if not by nature
then by descent), they are subject to regulatory administration in
many parts of the world. So you might simply not be allowed to
introduce a new PID since you haven't registered it with your
regulator. Of course you can always register a new one, but that takes
away any dynamicity (which we probably will want).

Another constraint are the commercial arrangements and business models
of network operators and service providers (duh, I managed to say the
nasty 'C' and 'B' words in one sentence!). Often a (e.g. IP) service
provider rents a specific bandwidth on a specific PID from a network
operator. This approach could be favorable to both of them since it
will then be easier to multiplex in the (e.g. IP) service and provide
easier network planning for the operator. Additionally a malfunction
of the 'bought-in' service will be much less likely to affect other
services.

Some service providers have the model that they feed their service to
as many (DVB) distribution networks as possible. In the above
mentioned scenario (renting a specific PID), their service need not
be taylored to the specific distribution network and they are
(almost) the sole responsible for the functioning or malfunctioning of
their service, as blunt PID remultiplexing today is as common and
reliable as - say - sliced bread.

As you can see there are many implications, boundary conditions and
limitations due to the fact that DVB networks are being operated as
television distribution networks and not as generic interconnection
networks. The section filtering invented by MPEG and adopted by DVB is
especially well suited for these (TV) broadcast medium environments
where remultiplexing comes into play.

> 2) MAC address filtering - we NEED this to run routing protocols,
> do we need it for directly connected end hosts? If hardware
> filtering is indeed required, could it not use the IPv4 / IPv6 header?
> Is this good / bad?
>
> > I cannot imagine, that a standard receiver filters at IP or
> > similar levels in software. MPE has the MAC address field, which tells
> > the local hardware to set a section level filter. The "minimal header
> > has no such capability. Will receivers get all packets on that PID ?
>
> Yes, currently they would.
>
> > How do you build groups of receiver devices ?
>
> Use another PID?
> [...]

No (for the above mentioned reasons). That is - amongst others - why
DVB crafted a solution to convey information about IP addresses being
targetted by specific streams or services. I am currently working on
getting clearance for forwarding the latest draft of this to you.

Best regards,

  --alexander adolf
    Chairman DVB GBS

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Alexander Adolf, Dipl.-Ing.(FH) --------------------------------------
Concept Engineer -----------------------------------------------------
System Software ------------------------------------ info@micronas.com
Micronas Gmbh - Munich Office ----------------------- www.micronas.com